Did you ever realize for how many food products we need microorganisms to create them? From bread to beers and wines,cheese, sausages, kombucha and many more!
During the process called fermentation, sugars are transformed into a new product through reactions carried out by micro-organisms.
They are real masterchefs!
Lactic acid bacteria
Lactic acid bacteria play a crucial role in both conventional and natural winemaking processes. They are responsible for the malolactic fermentation, a secondary fermentation that occurs after the primary yeast fermentation. Malolactic fermentation converts harsher, tart-tasting malic acid (naturally present in the grapes) into softer lactic acid. This process can reduce acidity and contribute to the wine's texture and flavour profile.
Natural wines are often produced using organic or biodynamic farming practices and follow a more traditional and hands-off approach to winemaking. The presence of indigenous or native yeast and bacteria is often encouraged. These are the naturally occurring yeast and bacteria present in the vineyard and winery environment. They can impart unique flavours and characteristics to the wine, reflecting the local terroir. This approach may lead to unpredictable results, making it even more fascinating to unravel the bacterial diversity present.
Cocoa (powder) and chocolate are products that are processed from fermented cocoa beans. Raw cocoa beans have an unpleasant taste and flavour, and fermentation, drying and roasting is necessary to obtain the desired characteristic cocoa and chocolate flavour, aroma and taste.
Fermentation of cocoa beans start spontaneously after removal of the beans and the viscous pulp from the cocoa pods. The fermentation generally lasts for 3 up to 6 days and consists of a yeast fermentation (24-48h, anaerobic, ethanol peak), a lactic acid bacteria fermentation (24-72h, microaerophilic, lactic acid peak) and an acetic acid bacteria fermentation (24-112h, aerobic, acetic acid and temperature peak).
The acetic acid and heat that are produced during the acetic acid bacteria fermentation (the temperature can go up to 50 °C) kill the beans and destroy the internal bean structure. This initiates an array of biochemical and enzymatic reactions that influence the bean colour and flavour development. It has been shown that hydrolytic enzymes inside the beans are activated by microbial metabolites such as acetic acid .
Although a high diversity of yeasts, lactic acid bacteria (LAB) and acetic acid bacteria (AAB) can be found in cocoa bean fermentations, it is assumed from research on fermentations in Africa, Asia and South America that only the prevailing species of each group are essential for the production of high-quality beans, i.e. Hanseniaspora opuntiae, Lactobacillus fermentum and Acetobacter pasteurianus, respectively. Spontaneous cocoa bean fermentations can result in excellent cocoa beans, if optimal practices are applied during fermentation. However, although the same restricted species diversity may be found, a difference in chocolate taste may occur. It is assumed that this is due to microbial variability, which appears to be influenced by farming practices such as box vs. platform, mixing vs. non-mixing of the fermenting cocoa pulp-bean mass. Research has revealed a direct correlation between AAB and LAB and the sour flavour in cocoa and chocolate, and between yeast and the fruity flavour of the end product. It is expected that inoculation with starter cultures may accelerate and stabilize cocoa bean fermentations. An added starter culture can dominate the cocoa bean fermentation process and hence influence the flavour of the cocoa beans and the cholocate produced thereof.
Swiss-type cheeses were originally manufactured in the Emmen valley (Emmental) in Switzerland; their precursors were various mountain cheeses. Emmental cheese is probably the best-known Swiss-type cheese and is frequently referred to simply as “Swiss cheese”. ‘Emmentaler Switzerland AOC’ has been registered since 2000 as an appellation d’origine contrôlée (AOC).
Three bacterial groups are used in the production of Emmentaler: Streptococcus thermophilus, Lactobacillus (mostly Lb. helveticus), and Propionibacterium freudenreichii (see picture). In the late stage of cheese production, P. freudenreichii consumes the lactic acid excreted by the thermophilic starters S. thermophilus and Lb. helveticus, and releases carbon dioxide gas, which slowly forms the bubbles that make holes. Failure to remove CO2 bubbles during production, due to inconsistent pressing, results in the large holes ("eyes") characteristic of this cheese.
The production of propionic acid by P. freudenreichii involves a complex metabolic cycle in which substrates are metabolized to pyruvate via glycolysis, pentose phosphate or the Entner-Doudoroff pathways, generating ATP and reduced co-enzymes. Pyruvate is oxidised to acetate and CO2 or reduced to propionate. There is increasing interest in the probiotic activity of P. freudenreichii as the bifidogenic compound it produces, 1,4- dihydroxy-2-naphthoic acid, stimulates growth of bifidobacteria. Supernatants or live freeze-dried strains of propionibacteria are commercially available as tablets to improve intestinal transit.
Reverse transcription quantitative PCR revealed persistency of thermophilic lactic acid bacteria metabolic activity until the end of the ripening of Emmental cheese. Falentin et al., Food Microbiology (2012)
The human body carries about 100 trillion microorganisms in its intestines, a number ten times greater than the total number of human cells in the body. Research suggests that the relationship between gut microbiota and humans is not merely commensal, but rather a mutualistic relationship. The intestinal microbiota members, their genes and their functions are collectively referred to as the gut microbiome.
Under ‘normal’ conditions, the microbiome ecosystem is in a state of metabolic homeostasis. This balance can be disturbed by factors related to diet, genetic background, the living environment and/or medical therapy, possibly leading to a state of dysbiosis. A range of mild (e.g. constipation, diarrhea) to serious (e.g. Crohn’s disease, obesity) clinical disorders are associated with over- and/or underrepresentation of key members of the gut microbiome.
Probiotics are live microorganisms (bacteria or yeasts) which, when administered in adequate amounts, confer a health benefit for the host. Probiotics have the potential to interact with the host through microbiological, metabolic and/or immunological effects, and are increasingly considered for preventive or therapeutic use in cases of gut dysbiosis.
About 2000 different yeast species have already been discovered and many more are estimated to exist. living with, cultivating, and using yeasts in food preparations long before we knew of the existence of microorganisms. Many different yeast species are involved in lesser-known food fermentations such as sourdough, kefir, certain cheeses, meat, soy, cocoa, coffee and many traditional fermented foods from all around the world. A common characteristic of yeasts found in fermented food is their generation of not only basic carbon dioxide and ethanol, but also of a huge number of substances that define the taste and the smell of the food.
Yeasts also produce certain enzymes, biological catalysts that are necessary the degradation of large molecules. For example, brewing yeasts produce the enzyme maltase that breaks down maltose, the main sugar found in grains, into glucose, consumed by the yeast. A yeast frequently found in sourdough, Wickerhamomyces anomalus, is producing phytase, which breaks down complex phosphor-containing molecules abundant in plants into bio-available phosphorus, an essential component of animal and human nutrition.
Some yeast species that occur naturally on fruit surfaces have been observed to restrict the growth of filamentous fungi. A few of them (e.g. Metschnikowia fructicola, Yarrowia lipolytica) have been developed into registered biocontrol products that may be applied on fruits such as citrus fruits, banana, apples, strawberries and grapes to prevent fungi from destroying valuable food resources.
To sum up, yeasts make raw foods easier to digest, enrich them in aromas, and protect them from spoilage. Yeasts are a driving force to enrich the diversity and nutritional value of our foods.
Alcoholic fermentations are carried out by yeasts, microscopic single-celled fungi, living of sugars that they convert into carbon dioxide and alcohol to gain energy. The fermentative power of yeasts differs among species. The best-known yeast species Saccharomyces cerevisiae has been selected over thousands of years for its high fermentative power. Certain groups of S. cerevisiae strains are particularly well suited for baking by their high carbon dioxide production and other groups of S. cerevisiae strains have evolved to be particularly resistant to alcohol, metabolic product and toxin at the same time. A yeast needs to be alcohol resistant to make wine and beer from fruits and grains.
Sourdough bread is a bread made by the fermentation of dough using wild lactic acid bacteria and yeasts. After ripening, a small part of the dough is used to provide the starter culture for a next batch of dough, a process called "backslopping". The presence of lactic acid bacteria results in a more sour taste compared to regular baker's bread, which is leavened by the yeast Saccharomyces cerevisiae alone. The lactic acid provides the bread with a longer shelf life and a reduction of phytic acid, which otherwise acts as a chelator of important minerals and niacin.
Sourdough was the usual form of leavening bread until the Middle Ages, when it was replaced with the foam from the beer brewing process, and ultimately by cultured yeast in the late 19th century. It is still an important way of leavening rye bread, since rye does not contain enough gluten for baker's yeast.